1. Field of the Invention
This invention relates to a line tracking system for automatically directing a vehicle along a predetermined path and more particularly to code circuitry for controlling the operation of the vehicle as it moves along the guide line.
2. Description of the Prior Art
A variety of automatically controlled devices for vehicles have been developed. One particularly advantageous type of vehicle control mechanism is disclosed in co-pending U.S. patent application, Ser. No. 489,043, filed July 16, 1974 now U.S. Pat. No. 3,935,922. The control circuitry for this vehicle is described also in applicant's co-pending U.S. patent application Ser. No. 488,961, filed July 16, 1974 now U.S. Pat. No. 3,970,840. Both applications are owned by the same assignee as the present application. The present invention comprises code circuitry for controlling the operation of a vehicle as it is guided along the guide path and is used in connection with the vehicle guidance mechanism disclosed in the foreging patent applications. For purposes of the present application, the drawings and descriptions of the guidance mechanism in these patent applications are hereby incorporated by reference. These patent applications will hereinafter be referred to as the "Related Applications".
Heretofore, a variety of code sensing devices have been employed for controlling the stopping and starting of other operations of an automatically controlled vehicle along a guide line or guide path. In Wesener U.S. Pat. No. 3,628,624, magnetic markers are used to route a vehicle as it approaches a junction in a guide path, with the vehicle being programmed prior to reaching the junction and the selected branch followed in accordance with the programming and signal received. In Hamilton U.S. Pat. No. 2,520,680, a code marker deposited in a plowed field indicates the location where a seed is to be deposited by a corn planter. In Braun U.S. Pat. No. 2,074,251, a code adjacent a guide line is used to provide visible or audible signals to the driver of the vehicle. In Kohls U.S. Pat. No. 3,411,603, a code signal is generated by magnets implanted adjacent the guide line. In Sampey U.S. Pat. No. 3,642,087, speed and position of a vehicle are controlled by counting diamond-shaped patterns forming a guide line. In Saunders et al U.S. Pat. No. 3,218,461, black dots on a white guide line are employed to mark distinct positions along the guide line. In Rabinow et al U.S. Pat. No. 3,172,496, a tuned circuit is employed for detecting code information in a video signal. In Kubo U.S. Pat. No. 3,738,443, the operation of a vehicle along a guide path is controlled by a series of equally spaced electrical or optical signals which are counted and compared to a reference count for controlling vehicle operation. Paulus et al U.S. Pat. No. 2,317,400 discloses a wire following system wherein the guide line is displaced to the side of the guide path at positions along the guide path to activate coding pickup cells.
In capacitive, inductive, or magnetic systems, the code markers are of distinctive character and not easily misrepresented by random surface irregularities or background radiation. However, in an optical tracking system, there may be sufficient reflectance or fluorescence in random areas adjacent the guide line that could be interpreted as a code marker. This is particularly true for high performance optical tracking systems that are designed to follow extremely bright to extremely dim guide lines, such as the guide lines employed in the Related Applications, where guide line intensity can vary by three orders of magnitude or more.
In most code marking systems, the presence of a code marking signal is determined by the increase in the intensity of code radiation received by a code sensor when the code sensor passes over a code mark. This type of system essentially operates on the basis of a comparison of the amount of code radiation present in the background surface and in the code marker. No means are provided to adjust the gain of the code cell to compensate for differences in code marker radiation intensity or in contrast between the code marker and the background. The only way in which such a system can detect dim lines or poor contrast conditions is to maintain an extremely high code cell gain at all times, and this high gain increases the probabilities of actuation of a code signal through random or spurious signals received by the code cell.
It is one object of the present invention to provide a code circuitry mechanism that can effectively detect a code marker even though the intensity of radiation received from the code marker may vary widely over several orders of magnitude, while at the same time limiting gain to the extent possible in order to prevent the production of code signals by spurious sources.
Another object of the present invention is to provide a code circuit that discriminates between valid code marker signals and any spurious signals that are detected to ensure that no operational signals are produced by the spurious signals.